I have played with the briefing map and think I have it working. There is a link below to a beta mod. Put into your MODS folder and install with JSGME (or install by hand if desired).
Briefing Map beta This is basically just Chief's improved map, resized to 1840x1840. I overlaid it on the original and tweeked it bit to line the coastlines up.
Please test and let me know if it works or not, problems, etc.